Medullary nail

ABSTRACT

A medullary nail (10) has a cavity (12) in which an inner part (20) can slide longitudinally without being able to rotate. The wall (11) of the medullary nail (10) which forms the cavity (12) is traversed on opposite sides by an elongated hole (16) in the region of the driving-in end (14). At least one fastening hole (22) aligned flush with the elongated hole (16) is provided in the inner part (20). When the connecting screws are driven into the spaced fastening holes (15, 16, 22) and an osteotomy is located between the connecting screws (15, 22), the edges of the osteotomy are moved apart as the inner part slides longitudinally, and the slowly widening gap between the edges of the osteotomy becomes filled with bone tissue.

The invention relates to a medullary nail having, forming a cavity, awall having a tapering end, and having an insertion end and, disposed atintervals over its length, fixing holes which extend transverselythrough its wall.

It is already known that medullary nailing is used in the field of longtubular bones, following fractures, for settling the two end of thefracture in respect of each other after the fashion of an inner splint.For this, after the medullary cavity has been drilled out, the medullarynail is in most cases rammed home from the proximal end of themedullated bone and, once it is finally positioned, it is securedagainst axial displacement and twisting by a plurality of transversebolts which pass through the bone cortex and fixing holes in themedullary nail. Since the periosteum which encloses the outside of thebone is not damaged to any substantial degree with this type oftreatment, the nourishment which is important to the healing process isencouraged and infection obviated.

In the advanced stages of fracture healing, the locking pins on one sideof the fracture gap can be removed. An axial loading now results in thereleased part of the bone sliding toward the still pinned bone, whichthus produces an axial compression on the fracture gap, so that thenewly formed bone becomes solidified.

In the past, lengthening of tubular bones or bridging of defectsfollowing shattered breakages, an inflammation of the bone or after theremoval of tumours in the region of long tubular bones have been carriedout by means of external fixing systems. In such cases, the bone endsare held by bone screws or wires which are passed through the skin andconnected on the outside to a frame. By displacing the frame partsassociated with the relevant bone ends, by means of tension bolts orwire winches, a relative movement between the bone ends is necessarilyachieved, the minimal displacement distances being continuously bridgedby newly forming bone tissue. Both for extension and also for segmentaldisplacement, an osteotomy is necessary, and with segmentaldisplacement, the segment of bone which is separated is drawn into thedefective zone.

The prior art external fixing systems have an unfavourable forceapplication point so that tilting occurs and expensive patient-impedingstructures are needed and they constitute a constant risk of infectiondue to germs penetrating through the bone screws or the wires and theyresult in unattractive scars.

The problem on which the invention is based resides then in so modifyinga medullary nail that while it maintains its function of serving as aninner splint and providing stability, it does at the same time permit anaxial displacement of separate bone parts away from each other.

On a basis of the medullary nail of the type mentioned at the outset,this problem is resolved by an inner part, rotationally rigidly disposedin the cavity and which can be displaced longitudinally by a drive andby, provided in the region of the insertion end, a transverselycontinuous elongated hole either in the oppositely disposed sides of thewall forming the cavity or in the inner part and by at least one fixinghole aligned with the elongated hole, either in the inner part or in theoppositely disposed sides of the wall forming the cavity.

The drive for longitudinal displacement of the inner part into thecavity may be a mechanical, pneumatic or hydraulic or also an electric,electromagnetic or piezoelectric drive which is installed inside and/oroutside the cavity. For example, in the case of a closed cavity, theinner part may take over the function of a piston adapted forlongitudinal displacement in the cavity and which in a predeterminedmanner is subjected to pressure which produces the requireddisplacement. By means of a pneumatic spring, a longitudinaldisplacement is also possible.

If the inner part is provided with an internally screwthreaded boreextending from one of its ends and if at the insertion end a rod with anexternal screwthread is rotatably mounted and is in screw-threadedengagement with the internal screwthread in the bore in the inner part,then the rotation of the rod can be accomplished by a rotary drive inthe form of a flexible shaft which, after a sufficiently long paththrough the soft tissue is guided outwardly through the skin and whichis provided at its proximal end with a hexagon for rotation. As a rotarydrive, it is also possible to use a suitable geared electric motor whichis flanged on the proximal end of the medullary nail or which can evenbe accommodated in the lumen of the medullary nail. The power can besupplied by batteries which are integral with the electric motor orseparately by implanting a battery housing into the subcutaneous fattytissue, a flexible conductor being used for connection. The electricmotor can be activated by the application of a magnet by means of a reedcontact or in continuous operation.

After drilling out the medullary cavity and applying an osteotomy at asuitable place with an internal saw, the medullary nail constructedaccording to the invention is driven in and in fact if the elongatedhole is disposed in the oppositely disposed portions of the wall of themedullary nail, only sufficiently that it projects from the insertionpoint by the amount by which the bone is to be lengthened. Once thelocking pins have been applied on either side of the osteotomy, then, bylongitudinal displacement of the inner part, distraction of the boneends at the osteotomy site is accomplished.

If the medullary nail is used for a segmental displacement, it may benecessary for the proximal bone portion to be separately secured againstaxial displacement. To achieve this, there is provision for widening outtowards the insertion end the wall which forms the cavity, and in theregion of this widening out, strip-forming U-shaped cuts are made, theend connecting portions of which are towards the insertion end of thenail. By means of a wedge element disposed for axial displacement in thecavity and engaging these strips, the strips can be spread apartoutwardly and enter into a form-locking connection with the proximalportion of the medullated bone, so that this latter is secured againstaxial displacements.

In known manner, the cavity in the medullary nail may be wholly orpartially open, preferably in the tapering zone but it can however alsobe completely closed and may have a cylindrical, polygonal or other kindof cross-section, for example a clover leaf cross-section.

Examples of embodiment of the invention will be explained in greaterdetail hereinafter with reference to the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a first embodiment of medullary nail;

FIG. 2 is an axial section through the medullary nail in FIG. 1;

FIG. 3 is a perspective view of a second embodiment of medullary nail;

FIG. 4 is an axial section through the medullary nail in FIG. 3;

FIG. 5 is an exploded perspective view of the parts of a modifiedinsertion portion of the medullary nail, and

FIG. 6 shows the insertion portion of the medullary nail in FIG. 5assembled and in an opened-out state.

The medullary nail 10 shown in FIGS. 1 to 6 has, forming a cylindricalcavity 12, a wall 11 of which a widening out insertion end 14 isprovided with an inset 17 while its other end 13 tapers to a nail point.The insert 17 has a central bore 18. In the wall 11 of the medullarynail 10 there are in the region of its tapering end 13 spaced apartfixing holes 15 which extend transversely through it.

In the cylindrical cavity 12 of the medullary nail 10 a cylindricalinner part 20 is longitudinally displaceable, secured against rotationand coaxially with the axis 40 of the medullary nail 10. Extending fromthe end face of the inner part 20 which is towards the wideninginsertion end 14 there is, coaxially in the inner part 20 a bore 21 withan internal screwthread into which is screwed the external screwthread33 of a rod 30 which extends through the bore 18 in the insert 17,ending in a head 31 with a recessed hexagonal socket 32. Rotation of thehead 31 displaces the inner part 20 axially within the cavity 12 of themedullary nail 10.

Where the embodiment shown in FIGS. 1 and 2 is concerned, there is inthe distance from the end of the bore 21 with the internal screwthread afixing hole 22 which extends transversely through the inner part 20.Aligned with this fixing hole 22 there is in the wall 12 of themedullary nail, on the oppositely disposed sides, an elongated hole 16.The medullary nail 10 in the embodiment shown in FIGS. 1 and 2 is drivenin to the extent that proximally it extends from the point of insertionby the amount of bone which is to be lengthened. After application ofthe locking pins, not shown, through the fixing holes 15, which aredisposed on one side of the osteotomy, and through the oppositelydisposed elongated holes 16 in the wall 12 of the medullary nail 10 andthrough the fixing hole 22 on the other side of the osteotomy, byrotation of the head 31 of the rod 30 the edges of the osteotomy aregradually removed from each other, the widening gap which leads to anextension of the bone being filled with newly formed bone tissue.

In the case of the embodiment shown in FIGS. 3 and 4, the wall 12 of themedullary nail 10 is parted at a joint 19 so that the two parts of themedullary nail 10 which are thus formed are displaceable in respect ofeach other on the inner part 20 in an axially guided manner. With thisembodiment, the elongated hole 16 is constructed in the inner part 20while in the wall 12 of the insertion portion of the medullary nail 10there are in the longitudinal extension in each case two spaced apartaligned and transversely extending fixing holes 22 on the oppositelydisposed sides in the inner part 20, aligned with the elongated hole 16.Where this embodiment is concerned, the medullary nail 10 is rammedcompletely into the tubular bone without any proximal projection. Then,the locking pins are set, the osteotomy being disposed between theportion with the tapering end 13 and the portion with the widening outinsertion end 14 of the medullary nail 10.

In the case of a segmental displacement with an embodiment as shown inFIGS. 1 and 2, in order to secure the proximal bone segment separatelyagainst axial displacement, there are constructed in the widening zoneof the medullary nail 10 U-shaped incisions 52, the arms of which extendparallel with the axis 40 and the bottom connecting portions 53 of whichare towards the insertion end 14. By reason of the U-shaped incisions52, strips 51 are formed. Guided with external wedges on the rod 10 is asleeve-like wedge element 50 which, by rotation of a screw 54 maintainedin the insert 17 in screw-threaded engagement at the insertion end 14,is axially displaced and by its external wedges, the strips 51 arespread outwardly into the wedging position shown in FIG. 6, so that apositive closure with the proximal bone ends is achieved, together witha securing of its position.

We claim:
 1. A medullary nail, comprisinga wall forming a cavity whichhas a tapering distal end and a proximal driving-in end, spaced fixingholes extending transversely through the wall over its length, an innerpart disposed in the cavity without being able to rotate, which has anopening associated with at least one of the fixing holes extendingtransversely therethrough, a rod acting on the inner part with anexternal thread for a longitudinal displacement of the inner part andthe wall upon rotation of the rod, altering the distance between thefixing holes, an insert (17) with a central bore (18) mounted at theopening of the driving-in end of the cavity, said rod (30) beingrotatably mounted and extending through the central bore (18), and anexternal thread formed on the rod (30) and being in screw-threadedengagement with an internal thread provided in a coaxial bore (21) inthe inner part (20), wherein the parts of a bone secured to the wall(11) on the one side, and the inner part (20), on the other side,gradually become separable from each other while forming a widening gapwhich becomes filled with new bone tissue.
 2. The medullary nail ofclaim 1, wherein the inner part (20) is longitudinally displaced intothe cavity (12) and adapted to be driven by a mechanical, pneumatic,hydraulic, electric, electromagnetic, or piezoelectric drive locatedwithin or outside the cavity.
 3. The medullary nail of claim 2, whereinthe wall (11) forming the cavity (12) is divided longitudinally by aseparating groove (19), and the two sections of the wall (11) thusformed are axially guided and displaceably mounted on the inner part(20) and are provided with fixing holes (15, 22), and the openingextending transversely through the inner part (20) is an elongated hole(16).
 4. The medullary nail of claim 3, further includingstrips formedby U-shaped cuts made in the driving-in end of the wall, and wedge meanshoused in the cavity for wedging the strips outwardly.
 5. The medullarynail of claim 2, wherein one of the fixing holes in the wall (11)associated with the opening (22) of the inner part (20) is an elongatedhole (16).
 6. The medullary nail of claim 1, wherein the wall (11)forming said cavity (12) is divided in a longitudinal direction by aseparating groove (19) into a first section and a second section, thefirst section and the second section of the wall (11) are axially guidedand displaceably mounted on the inner part (20) and are provided withfixing holes, and the opening extending transversely through the innerpart (20) is an elongated hole (16).
 7. The medullary nail of claim 1,wherein one of the fixing holes in the wall (11) associated with theopening (22) of the inner part (20) is an elongated hole (16).
 8. Themedullary nail of claim 1, further includingstrips formed by U-shapedcuts made in the driving-in end of the wall, and wedge means housed inthe cavity for wedging the strips outwardly.